<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #reult {
            width: 200px;
            height: 100px;
            border: 1px solid red;
        }
    </style>
</head>

<body>
    <div id="reult"></div>
    <script>
        const reult = document.getElementById("reult");
        //绑定事件
        reult.addEventListener("mouseover", function() {
            // 1.创建对象
            const xhr = new XMLHttpRequest();
            // 2.初始化    设置类型与url
            xhr.open('POST', 'http://127.0.0.1:8080/server');
            //设置请求头
            xhr.setRequestHeader('Content-Type', 'appliction/x-www-from-urlencoded')
                //3.发送
            xhr.send('a=100&b=200&c=300');
            //4.事件判定
            xhr.onreadystatechange = function() {
                if (xhr.readyState === 4) {
                    if (xhr.status >= 200 && xhr.status < 300) {
                        reult.innerHTML = xhr.response;
                    }
                }
            }
        });
    </script>
</body>

</html>